C++ On linux.

you could try here . you might find the standard free compiler that is installed by default on all linux boxes.
as long as you are not looking at compiling a commercial app with it.
( the gpl won't allow for any commercial usage )

You can compile commercial apps with GCC (g++,etc.) all you want. If you modify the GCC compiler itself, you need to release your changes, but you can compile closed source programs using GCC, under Linux if you so desire. I'd second using KDevelop with GCC, great combo.

If your up for a challenge, i'd also look into "VIM", but this is fairly advanced, but will pay off in the long run.